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# Test data overview

By default, every virtual user sends requests with the same data during a performance test. You can provide test data to vary the behavior of virtual users and better simulate real-world traffic, for example by giving each virtual user a unique login, token, or payload.

## Data files

Upload a CSV or JSON file when configuring a performance test. Each row in the file maps to one virtual user. Data files are a straightforward option when you have a fixed set of values and don't need to share or reuse the data across other Postman workflows.

Learn more at [Use a data file to simulate virtual users](/docs/tests-and-scripts/performance-testing/test-data/performance-test-data-files/).

## Datasets

Use a Postman dataset and view as your test data source. Datasets are queryable and shared across workflows, so the same data can power collection runs, mock servers, and performance tests without duplication. You can also control how rows are distributed across virtual users using iteration strategies.

Learn more at [Use a dataset to simulate virtual users](/docs/tests-and-scripts/performance-testing/test-data/performance-test-dataset/).